What is wrong with my Startup.ConfigureServices that is causing JWT Bearer authentication not to work?

I have been trying to implement "PwdLess" as a simple passwordless authentication mechanism for my ASP.Net Core 2.2 application. It is successfully generating JWTs which I am trying to use on the backend API of my application, with the JWT passed in via Authorization: Bearer <token>.

In my Startup.ConfigureServices method, I have the following code:

            // JWT authentication
                services.AddAuthentication(JwtBearerDefaults.AuthenticationScheme)
                .AddJwtBearer(JwtBearerDefaults.AuthenticationScheme, options =>
                 {
                     options.TokenValidationParameters = new TokenValidationParameters

                    {
                        ValidateIssuer = true,
                        ValidateAudience = true,
                        ValidateLifetime = true,
                        ValidateIssuerSigningKey = true,

                        ValidIssuer = "MYISSUERSTRINGHERE"
                        ValidAudience = "MYAUDIENCESTRINGHERE"
                        IssuerSigningKey = new SymmetricSecurityKey(
                        Encoding.UTF8.GetBytes("MYSECRETHERE"))
                    };
                });

            // ASP.NET Core MVC 
            services.AddMvc();

In the controller, on the method I want to authorize access to, I have:

        [Authorize]
        public IActionResult SomeMethod()
        {
        }

This throws a 401, which is confusing... Even more so because if I use the following code in my controller instead, everything works as expected:

        [Authorize(AuthenticationSchemes = JwtBearerDefaults.AuthenticationScheme)]
        public IActionResult ValidateToken()
        {
        }

I don't understand what I'm missing from my Startup.ConfigureServices that makes the AuthenticationSchemes value necessary on my Authorize attribute!

Please can you shed some light on the error of my ways?